In dieser Arbeit wird die Bildgebung durch eine Compton-Kamera zur Überwachung der Partikelstrahlentherapie erstmals an der Technischen Universität Dresden untersucht. Die inhärenten Beschränkungen der Methode wurden durch Berechnungen und Monte Carlo Simulationen studiert. Im Zuge dieser Untersuchungen erschien der Raumtemperatur-Halbleiter Cadmium Zink Tellurid als ein vielversprechendes Detektor-Material. Zur weiteren Untersuchung wurde eine einfache Compton-Kamera konstruiert bestehend aus einem Cadmium Zink Tellurid Detektor und einem ortsempfndlichen Szintillationsdetektor. Das System hat gezeigt, dass eine akkurate Bildgebung mit radioaktiven Punktquellen unter Laborbedingungen möglich ist. Weitere praktische Beschränkungen der Compton-Bildgebung unter Strahlbedingungen konnten durch Experimente an einem Protonen-Strahl hergeleitet werden. Durch die experimentellen Erfahrungen mit der in dieser Arbeit entwickelten Compton-Kamera konnten wertvolle Informationen gesammelt werden, die erlauben, die Bildrekonstruktion zu evaluieren und dazu beitragen, die weitere Forschung hin zu einer klinisch anwendbaren Compton-Kamera zu leiten. / This work presents the first efforts at the Dresden University of Technology to study the feasibility of Compton imaging as a modality to monitor ion beam radiation therapy. The inherent limitations of the method have been studied by means of calculation and Monte Carlo simulation. As a result, the room-temperature semiconductor cadmium zinc telluride appeared as a promising detector material for a clinical device. For more detailed investigation, a simple Compton camera has been constructed comprising a cadmium zinc telluride detector and a position sensitive scintillation detector. This system has proven that accurate imaging of radioactive point sources in the laboratory is feasible. More practical restrictions of Compton imaging in beam conditions have been derived through experiments at a proton facility. Through the experimental work with the Compton camera developed in this work, valuable information was gathered which allowed to test the image reconstruction and to direct the further research towards a clinical Compton camera system.

Low-energy X-rays in the range 10 - 50 keV have a wide application. One important application in radiological diagnostics is mammography, whereas, in radiotherapy, they are used for irradiation of superficial tumours, in brachytherapy and photon activation therapy. The importance of soft X-rays for fundamental radiobiological research is based on the fact, that all species of ionizing radiation produce a wide spectrum of secondary electrons, mainly responsible for the primary damage to be transformed into an observable radiobiological effect. By variation of the primary soft X-ray energy, a variation in the secondary electron spectra and therefore in the local energy deposition is provided. However, up to now no definitive conclusions about the relative biological effectiveness (RBE) of soft X-rays can be made due to its dependence on the photon energy, biological endpoint and dose range and the consequent large spread of the published data. The superconducting electron linear accelerator of high brilliance and low emittance (ELBE) at the Forschungszentrum Rossendorf with an electron energy up to about 40 MeV is used, among all, to generate X-rays in a wide energy range. One method for production of intensive, quasi-monochromatic X-rays in the energy range 10 - 100 keV tunable in energy, is by channeling of electrons in a perfect crystal. This X-ray source has many advantages over the most widespread X-ray source, which is the X-ray tube. Although the physical basis of the channeling effect has been previously investigated, the feasibility of an X-ray source based on channeling radiation (CR) for radiobiological studies has been for the first time theoretically and experimentally studied and a dedicated CR source built and optimised in the frame of this thesis. CR has been theoretically characterised in order to estimate its applicability for radiobiological studies. A good agreement between the theoretical predictions and the measured data has been found. The intrinsic properties of the CR source have led to the conclusion that monochromatisation is necessary. A monochromator based on HOPG mosaic crystals, was designed and manufactured. The dosimetrical methods have been investigated at the CR source as well as at an X-ray tube. Absolute dose measurements using an ionisation chamber and spectral dose distribution determination using semiconductor detectors have been performed. In addition, an unconventional system based on thermally stimulated exoelectron emission (TSEE) detectors, allowing to measure dose in a small volume and in the real cell environment has been tested and has proven itself appropriate in a variable dose range and in a liquid environment, in cases where reproducible laboratory conditions are provided. The biological endpoints clonogenic cell survival and micronucleus induction have been optimised for two established cell lines. The human mammary epithelial cells MCF-12A have been chosen due to the importance of RBE of soft X-rays for determination of risk from mammography. On the other hand, the use of the widespread mouse fibroblast cell line NIH/3T3 allows to compare the results with previously published data. The influence of the specific irradiation procedure at ELBE on the control level of cell survival and micronucleus induction has been tested and an irradiation system was developed and constructed. In addition, the RBE for soft X-rays was determined by X-ray tube irradiation at the Medical Department of Technische Universität Dresden. The RBE of 10 kV and 25 kV X-rays relative to 200 kV X-rays was determined. The RBE was found to be in the range from 1.0 to 1.4, depending on the used radiation quality, cell line and the biological endpoint, in agreement with previously published data for the same radiation qualities. These results confirm that systematical studies of RBE dependence on photon energy at the ELBE CR source are necessary and feasible.